Over the past century the demand for energy has grown exponentially. With the growing demand for energy, many different energy sources have been explored and developed. One of the primary sources for energy has been, and continues to be, the combustion of hydrocarbons. However, the combustion of hydrocarbons is usually incomplete and releases non-combustibles and other pollutants that contribute to smog in varying amounts. As a result of the pollutants created by the combustion of hydrocarbons, the desire for cleaner energy sources has increased. With the increased interest in cleaner energy sources, fuel cells have become more popular and more sophisticated.
Fuel cells conduct an electrochemical reaction to produce electrical power. The typical fuel cell reactants are a fuel source such as hydrogen or a hydrocarbon, and an oxidant such as air. Fuel cells provide a direct current (DC) that may be used to power motors, lights, or any number of electrical appliances and devices. There are several different types of fuel cells, each using a different electrode, electrolyte and fuel combination.
Fuel cells typically include three basic elements: an anode, a cathode, and an electrolyte. The anode and cathode are electrically isolated by the electrolyte. The electrolyte prohibits the passage of electrons, which results in an electrical current that can be directed to an external circuit. Fuel cells are usually classified by the type of electrolyte which is used, and are generally categorized into one of five groups: proton exchange membrane (PEM) fuel cells, alkaline fuel cells (AFC), phosphoric-acid fuel cells (PAFC), solid oxide fuel cells (SOFC), and molten carbonate fuel cells (MCFC).
Some types of fuel cells operate efficiently only at high temperatures or in a high temperature environment. Consequently, there can be a significant time lag before power is produced when the fuel cell is first started and must heat up to the appropriate operating temperature. In order for a fuel cell to replace other electrical power sources, e.g., batteries, in functionality, the fuel cell must be able to start operating rapidly.
As a result, some fuel cells have included some means for heating the cell to allow the cell to more rapidly reach an efficient operating temperature. Several methods of producing the optimal operating temperature have been used in the past, e.g., external catalytic combustors, electrically powered heat sources, etc. However, these solutions also raise further issues with the design and use of the fuel cell. For example, the external catalytic combustor is typically quite large, requires significant startup time, and needs a separate method for the initial heating process, often electrical resistance. Electronic heat sources require significant amounts of power resulting in considerable mass and volume to contain the energy well (battery, capacitor or other) and cause an undesirable thermal expansion to occur between materials.